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721.
M. Lemoine-Goumard F. Aharonian D. Berge B. Degrange D. Hauser N. Komin O. Reimer U. Schwanke 《Astrophysics and Space Science》2007,309(1-4):379-384
In 2004 and 2005, the shell-type supernova remnants RX J1713.7–3946 and RX J0852.0–4622 were observed and detected with the
complete H.E.S.S. array, a system of four Imaging Cherenkov Telescopes located in Namibia and dedicated to the observations
of γ-rays above 100 GeV. The energy spectra of these two sources have been measured over a wide energy range and revealed an integral
flux above 1 TeV similar to that of the Crab Nebula. Their morphologies were resolved with high accuracy with H.E.S.S. and
exhibit a striking correlation with the X-ray images, thereby pioneering a technique of unambiguously identifying spatially
extended γ-ray sources. The results of the observations will be presented. Similarities and differences between these two sources will
be pointed out as well as possible implications.
M. Lemoine-Goumard, F. Aharonian, D. Berge, B. Degrange, D. Hauser, N. Komin, O. Reimer, U. Schwanke for the H.E.S.S. Collaboration 相似文献
722.
S. T. Trudgill H. A. Viles R. Inkpen C. Moses W. Gosling T. Yates P. Collier D. I. Smith R. U. Cooke 《地球表面变化过程与地形》2001,26(10):1129-1142
Microerosion meter (MEM) measurements of the surface height of the balustrade of St Paul's Cathedral, London, have been repeated in the year 2000 following earlier measurements in 1980, 1981, 1985 and 1990. Methodological sources of error mean that while the measurements were made to 0·0001 mm, the data are reliable to two decimal places. There was a reduction in the mean erosion rate on horizontal sites from 0·045 mm a?1 in the period 1980–1990 to 0·025 mm a?1 in 1990–2000. Decreases in atmospheric SO2 levels from 20–25 ppb in 1980–1982 to around 10 ppb in 1990–2000, offer a causal explanation. The surface topography evolved more erratically in 1990–2000 than before, with much, but not all, of the more microelevated areas showing greater, and often more variable erosion. There are also indications of less erosion and more surface rises in low‐lying microareas on horizontal sites which is interpreted as possible deposition and/or microfloral growth in wetter depressions, the pattern being largely absent on a well drained vertical site. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
723.
Arsenic contamination of ground and pond water and water purification system using pond water in Bangladesh 总被引:1,自引:0,他引:1
H. Yokota K. Tanabe M. Sezaki Y. Akiyoshi T. Miyata K. Kawahara S. Tsushima H. Hironaka H. Takafuji M. Rahman Sk. A. Ahmad M. H. S. U. Sayed M. H. Faruquee 《Engineering Geology》2001,60(1-4):323-331
This paper, firstly, shows the distribution of arsenic-contaminated groundwater in Samta village. This village, which is in Jessore district in Bangladesh, was chosen as a model village for investigating the mechanism of groundwater contamination. 90% of the tube wells in this village had arsenic concentrations above the Bangladesh standard of 0.05 mg/l. Tube wells with arsenic concentrations of over 0.50 mg/l were distributed in the southern part of the village with a belt-like shape from east to west. Secondly, groundwater distribution is discussed with respect to its flow and the high arsenic zone (As≥0.50 mg/l) agrees well with the drifting zone of the groundwater. Furthermore, arsenic-free water supply systems suitable for a small area in the village have been developed. A pond sand filter (PSF) system which purifies pond water is discussed in this paper. Prior to the construction of the PSF, the water quality in ponds was examined for arsenic levels. The inflow of drainage from the tube wells was found to be the major cause of arsenic contamination of pond water. The PSF installed in Samta is working very well and produces a good quality of treated water. 相似文献
724.
The microstructure of hematite-ilmenite exsolution intergrowth of a natural titanohematite crystal from a granulite has been
investigated in a transmission electron microscope equipped with an energy filter. Special emphasis is on quantitative compositional
mapping at the nanometre scale using electron spectroscopic imaging, as well as mapping the Fe3+ and Fe2+ valence distribution in the intergrowth. Quantitative point analyses by energy-dispersive X-ray analysis have been compared
with results from electron energy-loss spectroscopy and element-distribution mapping. The results indicate that the coexisting
compositions of the two phases (Ilm88Hem12 and Ilm16Hem84) are independent of the size of the exsolution. The application of quantitative mapping to determining diffusion profiles
around precipitates is demonstrated.
Received: 30 March 2000 / Accepted: 7 September 2000 相似文献
725.
R. J. Ryel E. Falge U. Joss R. Geyer J. D. Tenhunen 《Theoretical and Applied Climatology》2001,68(1-2):109-124
Summary Tree canopy water use and foliage net CO2 uptake (NPP) were simulated for a 31-year-old Pinus sylvestris (Scots pine) plantation near Hartheim, in the Upper Rhine Valley, Germany with a mechanistically-based, three-dimensional
stand gas-exchange model (STANDFLUX) for a ten-day period during spring 1992. STANDFLUX was formulated to include the effects
of penumbra caused by the fine structure of the needles on light distribution within crowns. Good correspondence was found
between simulated rates of tree canopy water use when including penumbral effects and eddy-covariance ET and sap flow transpiration
measurements. Water use was 8–13% lower and NPP was 10–17% lower in simulations for the ten-day period when penumbral effects
were not included.
Simulated water use and CO2 uptake were compared with similar outputs from a simplified layer canopy model (including or not including penumbra) which
assumed horizontal homogeneity in canopy structure (GAS FLUX). Our results for the Pinus sylvestris stand indicate that penumbral effects were more important than the degree of model simplification with respect to foliage
distribution (three-dimensional vs. layered structure) for estimating stand-level fluxes for these pines.
Simulated maximum hourly NPP was similar to rates measured for other Pinus sylvestris stands using other methods. Predicted decreases in tree transpiration due to the modelled response of needle gas exchange
to increasing vapour-pressure deficit agreed with measured changes in transpiration, and suggested that stomatal response
may have been more important than decreasing soil water availability in controlling water flux to the atmosphere during this
period. The overall results of the study demonstrate that current approaches in canopy modelling that separate light into
sun versus shade intensities can be effective, but must be applied with caution when attempting to predict long-term water
and carbon balances of forests.
Received May 1, 1999 Revised November 9, 2000 相似文献
726.
—?The hydrostatic Naval Research Laboratory/North Carolina State University (NRL/NCSU) model was used to study the mesoscale dynamics and diurnal variability of the Intertropical Convergence Zone (ITCZ) over the Indian Ocean in the short-range period. To achieve this objective the initial conditions from two northeast monsoon episodes (29 January, 1997 and 29 January, 1998) were run for 48-hour simulations using a triple-nested grid version of the model with 1.5°?×?1.5°, 0.5°?×?0.5° and 0.17°?×?0.17° resolutions. The 1997 case represents a typical northeast monsoon episode, while the 1998 case depicts an abnormal monsoon episode during an El Niño event.¶Comparisons between the model-produced and analyzed mean circulation, wind speed, and associated rainfall for different spatial scales are presented. During the active northeast monsoon season in 1997, the major low-level westerly winds and associated high rainfall rates between 0° and 15°S were simulated reasonably well up to 24 hours. During the 1998 El Niño event, the model was capable of simulating weak anomalous easterly winds (between 0° and 15°S) with much lower rainfall rates up to 48 hours. In both simulations, the finest grid size resulted in largest rainfall rates consistent with Outgoing Longwave Radiation data.¶The model performance was further evaluated using the vertical profiles of the vertical velocity, the specific humidity and temperature differences between the model outputs and the analyses. It is found that during a typical northeast monsoon year, 1997, the water vapor content in the middle troposphere was largely controlled by the low-level convergence determined by strong oceanic heat flux gradient. In contrast, during the 1998 El Niño year moisture was present only in the lower troposphere. Due to strong subsidence associated with Walker circulation over the central and eastern Indian Ocean, deep convection was not present. Finally, the diurnal variations of the maximum rainfall, vertical velocity and total heat flux were noticeable only during the 1997 northeast monsoon year. 相似文献
727.
U. Schreiber M. Schneider C.H. Rowe G.E. Stedman W. Schlüter 《Surveys in Geophysics》2001,22(5-6):603-611
Ring laser rotation sensors are best known from inertial navigation, wherethey have many advantages over mechanical gyroscopes. They have recentlybeen greatly improved, and show potential as fully independent length-of-daysensors. We discuss some important aspects of current limitations in theirperformance. In particular we demonstrate a novel scheme for thestabilisation of a large ring laser against frequency pulling effectsinduced by backscatter. 相似文献
728.
D. W. Arlander D. Brüning U. Schmidt D. H. Ehhalt 《Journal of Atmospheric Chemistry》1995,22(3):243-249
A series of 72 measurements of the acetaldehyde (CH3CHO) mixing ratio were made in the lower troposphere during TROPOZ II. These measurements are the first ever made of the background level of this trace gas in the free troposphere. The data show a vertical decrease of the CH3CHO mixing ratio with increasing altitude and indicate higher CH3CHO concentrations in the Northern Hemisphere — in general agreement with a model-derived average CH3CHO distribution. Deviations of the observed CH3CHO mixing ratios from the modelled mean distribution are correlated with similar deviations in the corresponding HCHO mixing ratios. 相似文献
729.
Investigation on the Pollution Potential of Waterworks Sludges Several contaminated sludges from water treatment plants with known or estimated concentrations of trace elements were investigated for their leaching characteristics and long-term stability using standard and advanced test procedures. Potentially hazardous elements in the sludge are zinc, nickel, and arsenic with concentrations of up to 1.2 g/kg dry matter (mass). Preliminary sorption tests with synthetic sludge components like iron hydroxide, manganese oxide, silicate clay minerals, and chitine powder as a model organic component showed that Cu is associated with the organic phase wheras arsenic is predominantly bound to the iron oxide minerals. The recently suggested pHstat test procedure was used to assess the leaching characteristics of metals at typical pH values. This procedure was compared with the DEV-S4 test, the current standard test in Germany, consisting of a simple lixiviation of the solids with water, without pH control. The pHstat test yields results which are much better to interprete than those obtained by the DEV-S4 procedure. The iron and manganese sludges are well buffered against changes in pH and redox potential so that low pH values and/or reducing conditions can hardly occur. Thus, in deposited material a sudden leaching of heavy metals is unlikely and due to the presence of iron and manganese oxides the pentavalent arsenic is protected against conversion into the highly mobile trivalent form at neutral to low pH. Co-deposition with reducing organic matter and alkaline stabilisation material or waste (like fly ash) could influence the binding properties and should be strictly avoided. 相似文献
730.
Weathering rates were calculated using the height difference between lead lettering and marble on gravestones at three sites in the UK. Comparison of their regression lines and residuals suggested that two of the sites, Portsmouth and Wolverhampton, had similar amounts and rates of weathering over the last 100-150 years. Gravestones in Swansea appear to have weathered much more and much faster than gravestones at the other two sites. These differences may be the result of the differing pollution and rainfall histories of the three sites. 相似文献